Pyrolyzing hydrocracked naphthas to produce unsaturated hydrocarbons

ABSTRACT

1. IN A PROCESS FOR THE PREPARATION OF UNSATURATED HYDROCARBONS BY PYROLYSIS OF NAPHTHAS BOILING IN THE RANGE OF ABOUT 80 TO 450*F. IN A PYROLYSIS FURNACE, THE IMPROVEMENT COMPRISING HYDROCARCKING SAID NAPHTHAS AT FROM ABOUT 500 TO ABOUT 1000*F. AND ABOUT 600 TO ABOUT 3000 POUNDS PER SQUARE INCH GAUGE WHILE FEEDING ABOUT 20000 TO ABOUT 5000 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF NAPHTHA FED, TO FORM A MIXTURE OF PARAFFINS AND ISOPARAFFINS SAID MIXTURE CONSISTING ESSENTIALLY O HYDROCARBONS CONTAINING FROM 1 TO ABOUT 7 CARRBON ATOMS PER MOLCULE AND PYROLYZING THE RESULTING MIXTURE OF PARAFFINS MOLECULE AND PYROLYZING THE RESULTING MIXTURE OF PARAFFINS 800 TO ABOUT 1200*C.

Q 1974 c. c. ZIMMERMAN. JR. ET 3,839,434

PYROLYZING HYDROCRACKED NAPHTHAS TO PRODUCE UNSATURATED HYDRQCARBONS Filed July 17, 1970 LIGHT ENDS METHANE-RICH I LIGHT gRAlGHT RUN INAPHTHA TO PYROLYSIS LZE FUEL CRUDE STRAIGHT RUN D|STL TION Y SEPAR 0 OIL I LA NAPHTHA H DROCRACKER AT R HYDROGEN DIESEL a I F--l DISTILLATE FUEL COKER NAPHTHA METHANE-RICH FUEL I SEPARATION a PYROLYSIS REDUCED PURIFICATION FURNACES cnuoz COKER OILS a TARS ETHYLENE AND/OR ACETYLENE mzrnwrmcn FUEL United States Patent O 3,839,484 PYROLYZING HYDROCRACKED NAPHTHAS TO PRODUCE UNSATURATED HYDROCARBONS Carle C. Zimmerman, Jr., Littleton, and Perry A. Argabright, Sedalia, Col0., assignors to Marathon Oil Company, Findlay, Ohio Filed July 17, 1970, Ser. No. 55,799 Int. Cl. C07c 3/00 US. Cl. 260-683 R 10 Claims ABSTRACT OF THE DISCLOSURE Yields of unsaturated hydrocarbons, e.g. ethylene and acetylene, from pyrolysis furnaces are improved by first hydrocracking naphthas, e.g. straight-run naphthas or coker naphthas, and charging the resulting mixture or paraifins and isopar-aflins to the furnace. Hydrogen from the pyrolysis products can be recycled to the hydrocracker. Fuel from the pyrolysis products can be utilized to heat the pyrolysis furnace. Oils from the pyrolysis products can be recycled to a coker which produces coker naphthas for use in the process.

CROSS REFERENCES TO RELATED APPLICATIONS US. Pat. application Ser. No. 821,164 filed Apr. 25, 1969 now US. Pat. 3,617,495 and Ser. No. 819,171, filed Apr. 25, 1969 now U.S. -Pat 3,556,987 relate to the general field of the present invention BACKGROUND OF THE INVENTION (1) Field of the Invention The present invention relates generally to the field of hydrocarbon conversion processes. More specifically the invention relates to the field of chemistry of carbon compounds, hydrocarbons, acyclic, olefins from hydrocarbons by dehydrogenation, usually classed in United States Patent Ofiice Class 260-683.3.

-(2) Description of the Prior Art US. 3,143,490 produces more branched-chain paraftfins by dehydrogenating normal parafiins, then hydrogenating them to cause branching. US. 2,750,420 cracks hydrocarbons, producing ethylene and acetylene. Acetylene may be selectively hydrogenated to ethylene or ethane. Other patents of substantially less pertinance are: US. 1,460,545 (producing ethylene from pure ethane); U.S. 2,045,255 (producing ethylene under subatmospheric pressure); US. 2,274,204 '(oxydehydrogenating hydrocarbons); US. 2,354,892 (dehydrogenating hydrocarbons with activated alumina-tungsten oxide catalyst); US. 2,399,540 (oil soluble metal-organic catalyst for hydrocarbon conversion); U.S. 2,514,294 (specialized fractionation of mixed hydrocarbon products); U.S. 2,549, 240 (catalytic dehydrogenation of ethylene to acetylene); US. 2,629,753 (catalytic pyrolysis of ethane to ethylene); US. 2,653,903 (sequential cracking of petroleum fracti-ons); US. 2,877,279 (cracking apparatus); US. 2,924,- 632 (catalyst regeneration); and US. 3,437,585 (extraction process in combination with dehydrogenation).

SUMMARY '(1) General Statement of the Invention Naphthas, e.g. straight-run naphthas or coker naphthas or mixtures thereof are hydrocracked, and the resulting mixture of p'araffins and isoparaffins low in naphthenes and aromatics is charged to a pyrolysis furnace for the production of ethylene and/or acetylene and other unsaturated hydrocarbons. Hydrogen separated from product gas can be recycled to the hydrocracker, methanerich fuels from the product gas can be used to heat the pyrolysis furnaces, and tars and oils from the pyrolysis gas can be sent to a coker which produces coker naphtha for use in the product. The pyrolysis furnaces may be of the steam cracker type or of the Wulif type or of other conventional design.

The invention improves yields of ethylene and acetylene from pyrolysis furnaces. Tars, coke, and by-product diolefins and aromatics are reduced. Fouling the process equipment is substantially reduced. On-stream time between shut-downs for decoking of equipment is increased. Furnace life and ease of operation are increased.

(2) Utility of the Invention The present invention produces unsaturated hydrocarbons, e.g. acetylene, which can be hydrochlorinated to produce vinyl chloride for production of vinyl chloride polymers according to well-known techniques and ethylene which can be polymerized according to well-known techniques to produce polyethylene.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a schematic representation of a preferred embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS (1) Starting Materials The starting materials for the present invention are hydrogen produced by any conventional technique and utilized in the hydrocracking step; and naphthas, e.g. coker naphthas and straight-run naphthas. By naphtha is meant any hydrocarbon having a boiling range within the general range of from about F. to about 450 F., more preferably from about 80 F. to about 400 F. By coker naphtha is meant a naphtha produced as a byproduct from the coking of hydrocarbon residua, e.g. delayed petroleum coking. By straight-run naphtha is meant a naphtha produced by the distillation of crude oil. The preferred starting materials are hydrocarbons containing from 1 to about 7, more preferably from about 2 to about 6, and most preferably from 2 to about 5 carbon atoms per molecule. In general, normal and isoparaffins containing 25 carbon atoms have been found to be the best feeds for pyrolysis furnaces. Olefins are less desirable feed stocks. All feed stocks of 6 or more carbon atoms (particularly normal C and above) are less desirable than those of the 25 carbon number. The heavier feed stocks are less desirable because the yields of acetylene and ethylene are lower and the corresponding yields of coke, tars, and oils are greater. For carbon numbers of 6 or greater, normal and isoparaflins are the most desirable, olefins and naphthenes are less desirable, aromatic hydrocarbons are the least desirable. Feeds of 6 or more carbon atoms are susceptible to a side reaction of cyclization and aromatization. Aromatic formation is much less with feeds of 25 carbon atoms because it requires sequential bi-molecular reactions. Two-body reactions have a much lower probability of occurrence than uni-molecular reactions. The present invention permits the production of a feed stock consisting primarily of parafiins and isoparaifins in the 25 carbon number 3 range. This feed stock is therefore particularly well suited for use in pyrolysis furnaces.

(2) Hydrocracking Hydrocracking is accomplished in the range of from 500 to about 1000, more preferably 600 to about 900, and most preferably 700 to about 850 F. and 600 to about 3000, more preferably 800 to about 2000, and most preferably 1000 to about 1800 p.s.i.g. Liquid hourly space velocities in the range of from 0.5 to about 10, more preferably 0.5 to about 5, and most preferably 1 to about 3, feeding from 2000 to about 5000, more preferably 2500 to about 4500, and most preferably 3000 to about 4000 Standard cubic feet (SCF) of hydrogen per barrel of naphtha feed to the hydrocracker. Hydrocracking 18 more generally discussed in Hydrocracking Handbook; Reprinted from Hydrocarbon Processing. Gulf Publishing Company (1969) and Scott, J. W., Robbers, J. A., Mason, H. F., Patterson, N. J. and Kozlowski, R. H., Isomax Gives Gasoline or Distillate Hydrocarbon Processing & Petroleum Refiner, 42, 131-136 (July 1963) and in the references cited therein.

(3) Pyrolysis Pyrolysis in Wulif furnaces is generally accomplished at temperatures of from 800 to about 1200 C., with residence times at the peak furnace temperatures of 0.008 to about 0.02 secs. followed by extremely rapid quenching. Normally 1.5-3 lbs. of steam are fed to the furnace per lb. of naphtha charge. The Wulff Process pyrolysis is more fully described at page 384 of Miller, Acetylene, Its Property Manufacture and Uses. Steam cracking is accomplished at about 800-900 F. at a residence time of 0.2-1.0 sec. using about 0.2-1.0 lbs. of steam per lb. of feed. No catalyst is used and the cracking is done inside alloy tubes hung in a direct fired furnace. Steam cracking furnaces are more fully described at p. 125, of Miller, Ethylene and Its Industrial Derivatives.

(4) Examples The invention can be more fully understood by reference to the specific embodiment shown in the drawing. Crude oils fractionated in the distillation column 1 give five primary products: (1) light ends (mostly methane and ethane which can be sent to the plant fuel system), (2) light straight-run naphtha (C -C hydrocarbons which can be sent directly to the pyrolysis furnace), (3) straight-run naphtha (approximate boiling range 80-430 R, which provides feed to the hydrocracker in accordance with the invention), (4) diesel fuel and distillate fuels (boiling in the range of 400-650" F. and suitable for direct sale), and (5) reduced crude (boiling at 650 F. or above which can be sent to the coker) The straight-run naphtha containing mostly parafiins and naphthenes is sent to the hydrocracker 2 along with the naphtha produced by the coker. Only one stage is required in the hydrocracker. The hydrocracker operates at approximately 800 F, 1500 p.s.i.g., 2.5 liquid hourly space velocity, 4000 SCF hydrogen per barrel of naphtha feed and utilizes a nickel-molybdenum catalyst on a silica alumina support. The hydrocracker efiluent is sent to a flash drum 3 where hydrogen and methane are separated from the other products. The hydrogen can be recycled to the hydrocracker and the methane-rich fuel can be used as fuel for the pyrolysis furnaces or fed to the plant fuel system. The liquid efiluent, a mixture of propane, butane, isobutane and light gasoline fractions containing over 90% paraflins and less than aromatics and naphthenes, can be sent to the pyrolysis furnace 4. In addition, substantial sulfur and nitrogen removal has been accomplished in the hydrocracking.

The pyrolysis furnace 4 is a Wullf-type furnace operating at a center temperature of approximately 1200 C. with a residence time at peak furnace temperature of approximately 0.008 secs. and includes a rapid oil quench.

Feed to the pyrolysis furnace consists of a mixture of light straight-run naphtha from the distillation tower 1 and liquid products from the separator 3. 1.6 Lbs. of steam are mixed with each lb. of feed as it enters the furnace. This feed stock contains only small amounts of naphthenes or aromatics and is essentially olefin-free. In addition, the carbon range of the feed stock is substantially in the 2-5 carbon atom range with some 6-carbon atom molecules, but is essentially free of components having more than 6 carbon atoms.

In the pyrolysis furnace 4, the feed stock is cracked to a mixture of acetylene, ethylene, methane and hydrogen. Only a small amount of propylene, aromatic oils, and tars are produced. Separation and purification section 5 consists of distillation and scrubbing of products. The products produced by the total components of the invention are: acetylene and ethylene for sale; hydrogen for recycle to the hydrocracker furnace; methane-rich fuel gas used as fuel for the pyrolysis furnace; and a small stream of oils and tars sent to the coker 6.

If the hydrogen produced by the Wullf or other pyrolysis operation is not sufficient for the operation of the hydrocracker, additional hydrogen can be obtained by reforming a portion of the methane-rich gases recovered from the separations plant 5. This can easily be accomplished because the methane-rich gas is sulfur-free when it leaves the separations plant.

(5) Modifications of the Invention It should be understood that the invention is capable of a variety of modifications and variations which will be made apparent to those skilled in the art by a reading of the specification and which are to be included within the spirit of the claims appended hereto.

For example, while the above specific embodiment utilizes a Wullf-type pyrolysis furnace, a stream cracker of the type commonly used to produce ethylene can readily be substituted for use with the invention.

What is claimed is:

1. In a process for the preparation of unsaturated hydrocarbons by pyrolysis of naphthas boiling in the range of about to 450 F in a pyrolysis furnace, the improvement comprising hydrocracking said naphthas at from about 500 to about 1000 F. and about 600 to about 3000 pounds per square inch gauge while feeding about 2000 to about 5000 standard cubic feet of hydrogen per barrel of naphtha fed, to form a mixture of paraffins and isoparafiins said mixture consisting essentially of hydrocarbons containing from 1 to about 7 carbon atoms per molecule and pyrolyzing the resulting mixture of parafiins and isoparafiins in said pyrolysis furnace, at from about 800 to about 1200 C.

2. The process of Claim 1 wherein the unsaturated hydrocarbons comprise ethylene.

3. The process of Claim 1 wherein the unsaturated hydrocarbons comprise acetylene.

4. The process of Claim 1 wherein the naphthas are selected from the group consisting of straight-run naphthas and coker naphthas.

5. The process of Claim 1 wherein hydrogen is produced as a coproduct with said unsaturated hydrocarbons and said hydrogen is recycled to said hydrocracking step.

6. The process of Claim 1 wherein there is also produced as a co-product to said unsaturated hydrocarbons a methane-rich fuel gas which is used as at least a portion of the fuel for heating said pyrolysis furnace.

7. The process of Claim 1 wherein there is produced as co-products to said unsaturated hydrocarbons a stream of oils and tar which are sent to a coker which in turn produces coker naphtha for hydrocracking and thereafter charging to said pyrolysis step.

8. The process of Claim 1 wherein said pyrolysis furnace is a Wulff pyrolysis furnace.

9. The process of Claim 1 wherein the pyrolysis furnace is a steam cracker.

10. In a process for the preparation of ethylene and acetylene by pyrolysis of straight-run or coker naphthas boiling in the range of about 80 to 450 F. in a pyrolysis furnace, the improvement comprising hydrocracking said straight-run naphtha or said coker naphtha at from about 500 to about 1000 F. and about 600 to about 3000 pounds per square inch gauge while feeding about 2000 to about 5000 standard cubic feet of hydrogen per barrel of naphtha fed, to form a mixture of paraffins and isoparaffins, said mixture containing from 1 to about 7 carbon atoms per molecule charging the resulting mixture of paraffins and isoparaffins to said pyrolysis furnace operatmg at from about 800 to about 1200 C., producing hydrogen, methane-rich fuel gas, a stream of oils and tar,

said hydrogen for use in the hydrocracking step, recycling said methane-rich fuel gas for use in heating said pyrolysis furnace, and coking said stream of oils and tar to produce coker naphtha for charging to said pyrolysis step.

References Cited UNITED STATES PATENTS 7/1933 Pier et a1 20861 5/ 1965 Kozlowski et al. 208-59 1/1971 Zimmerman Jr. et al.

260-683 R 6/1941 Porter 23285 7/1969 Kniel 260683 9/1969 Kitzen 260-683 R 4/1941 Wulff 260679 8/ 1959 Davison 260683 D. E. GANTZ, Primary Examiner ethylene, and acetylene in said pyrolysis furnace, recycling 15 J, M NELSON, Assistant Examiner US. Cl. X.R.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,839,484 Dated October 1, 1974 O Inventor(s) Carle C. Zimmerman et al It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 16: Delete "or" and insert of-.

Col. 2, line 14: After "fouling" insert -of-.

Col. 3, line 33: Delete "800-900F." and insert therefor --800-900C.-.

Signed and Scaled this Twentieth Day Of September 1977 [SEAL] Attest:

RUTH C. MASON LUTRELLE F. PARKER Attesting Officer Acting Commissioner of Patents and Trademarks 

1. IN A PROCESS FOR THE PREPARATION OF UNSATURATED HYDROCARBONS BY PYROLYSIS OF NAPHTHAS BOILING IN THE RANGE OF ABOUT 80 TO 450*F. IN A PYROLYSIS FURNACE, THE IMPROVEMENT COMPRISING HYDROCARCKING SAID NAPHTHAS AT FROM ABOUT 500 TO ABOUT 1000*F. AND ABOUT 600 TO ABOUT 3000 POUNDS PER SQUARE INCH GAUGE WHILE FEEDING ABOUT 20000 TO ABOUT 5000 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF NAPHTHA FED, TO FORM A MIXTURE OF PARAFFINS AND ISOPARAFFINS SAID MIXTURE CONSISTING ESSENTIALLY O HYDROCARBONS CONTAINING FROM 1 TO ABOUT 7 CARRBON ATOMS PER MOLCULE AND PYROLYZING THE RESULTING MIXTURE OF PARAFFINS MOLECULE AND PYROLYZING THE RESULTING MIXTURE OF PARAFFINS 800 TO ABOUT 1200*C. 